This study will evaluate the effects of cocaine alone, and in combination with effective treatments for attention deficit hyperactivity disorder (ADHD) in subjects with current cocaine abuse histories. Based on the limited clinical literature we hypothesize that some individuals with ADHD may be using cocaine to "self-medicate" their ADHD symptoms. The first experiment will be carried out to test the hypothesis that adult cocaine users with ADHD-like syndrome have unique subjective responses to cocaine.